Monoclonal antibody therapy has provided an opportunity to target and destroy tumors using antibodies engineered against tumor-specific antigens. In general, monoclonal antibody therapy stimulates a patient's immune system to attack malignant tumor cells or prevents tumor growth by blocking or inhibiting specific cell receptors. Monoclonal antibodies used in cancer therapy generally target tumor-specific antigens on cell-surface molecules. Representative cell-surface molecules targeted in clinical trials include those originating from various lymphomas/leukemias (such as T-cell and/or B-cell lymphomas/leukemias) and solid tumors (such as epithelial tumors of the breast, colon, and lung).
Promising results have been reported in the treatment of breast cancer with humanized monoclonal antibodies, particularly treatments targeting the HER2 (neu/ErbB2) receptor.
HER2 is a transmembrane surface-bound receptor tyrosine kinase and is normally involved in the signal transduction pathways leading to cell growth and differentiation. HER2, also known as epidermal growth factor receptor 2, belongs to a family of epidermal growth factor receptors (EGFRs) including HER1 (ErbB1), HER3 (ErbB3), and HER4 (ErbB4) (Hudis, 2007, N Engl J Med 357(1):39-51). The ErbB receptors typically dimerize on ligand binding. Although HER2 has no known ligand, it is the preferential dimerization partner of other members of the ErbB family. (Hudis, 2007, N Engl J Med 357(1):39-51). Overexpression of HER2 results in the induction of angiogenesis, a component of cancer growth, and the evocation of an antitumor T-cell response (Ménard et al., 2003, Oncogene 22:6570-6578). HER2 is overexpressed in about one-quarter of breast cancer patients (Bange et al., 2001, Nature Medicine 7:548-552).
The development of a monoclonal antibody therapy based on the discovery of the role of HER2 in breast cancer first involved the development of a murine-based antibody. Researchers discovered that the murine monoclonal antibody 4D5 had a significant and dose dependent efficacy specifically for HER2 overexpressing cancer cells, while having no effect on cells expressing physiological levels of HER2. However, murine antibodies elicit an immunogenic response in human patients. Murine monoclonal antibodies can be humanized (thereby reducing the murine-induced immune response) by identification of a minimum set of amino acid residues in the complementarity determining regions (CDRs) of the murine antibody required for antigen specificity and antigen binding affinity and substituting these regions into the CDRs of a consensus human IgG framework. The framework regions are the non-CDR regions in the variable chains of the antibody. Accordingly, the murine (4D5) monoclonal antibody was humanized, resulting in a recombinant, humanized monoclonal antibody directed against HER2. This drug is commercially known as Herceptin® (trastuzumab), which gained FDA marketing approval in late 1998.
Herceptin® is known to bind with high affinity to the extracellular domain of the HER2 protein, thereby inhibiting the proliferation of human tumor cells that overexpress HER2. Herceptin® is also a mediator of antibody-dependent cellular cytotoxicity (ADCC) which has been shown to be preferentially exerted on HER2 overexpressing cancer cells compared with cancer cells that do not overexpress HER2.
Herceptin® can elicit an immune response when administered to humans. Such an immune response can result in an immune complex-mediated clearance of the antibodies or fragments from the circulation, and make repeated administration unsuitable for therapy, thereby reducing the therapeutic benefit to the patient and limiting the re-administration of the antibody. Further, Herceptin® may be contraindicated in patients with pre-existing heart disease. Herceptin® has been associated with cardiac dysfunction in 2-7% of cases (Borghesi et al., 2006, Immunol Res 36(1-3):27-32). Also, while up to 70% of HER2-positive breast cancers demonstrate a response to Herceptin®-based therapies, resistance almost inevitably arises within a year of the initial response. Finally, additional problems with tumor-specific or tumor-selective monoclonal antibodies such as Herceptin® as therapeutic agents include antigenic variation of the tumor, inefficient killing of cells after binding the monoclonal antibody, inefficient penetration of the antibody into the tumor mass, and soluble target antigens mopping up the antibody.
Accordingly, there is a need to provide improved monoclonal antibodies that interfere with the HER2 receptor that overcome one or more of these problems, for example, by generating variants with higher affinity than Herceptin® that can be administered at reduced dosages, or variants with reduced immunogenicity and other side-effects as compared to Herceptin®. Furthermore, there is a need to provide variants with increased expression in heterologous hosts, with increased solubility, with decreased heterogeneity due to glycosylation and/or with increased stability, e.g., with respect to oxidation, deamidation and/or cyclization of amino acids.
Citation or identification of any reference in Section 4 or in any other section of this application shall not be construed as an admission that such reference is available as prior art to the present disclosure.